Note: Gems and other precious stones are the ones which get set in the top of the pendant or rings. And they are just know by their names, like oh what a diamond ring, or a beautiful sapphire necklace.

Other related terms not to be confused with are :

Bail > a component of certain types of jewelry, mostly necklaces, that is used to attach a pendant or stone.,

@J.R., added pics to clarify what i was saying.
–
RaghavMar 29 '13 at 11:20

I don't think the bail is the hook per se, it depends on the type of bail used. There are donut bails, pinch bails, glue-on bails, wire wrapped bails, etc. You can find more information here, see more than 80 bails for sale here, or watch this video to see that not all bails have hooks.
–
J.R.Mar 29 '13 at 17:54

@J.R., The first link you suggest is giving this information/what should we infer from it?? > A jewelry bail is a jewelry making component (findings) that attaches a pendant to a necklace, chain, cord etc. > And also, if we go through all the images in the second link provided by you, same is the result, something to hold or latch from.
–
RaghavMar 29 '13 at 17:58

Raghav, here is what you said in your answer: "Bail > the hook." Here is what you said in your comment to Matthew: "it is the hook" [emphasis in the original]. Here is what you said in a comment to me: "i meant bail is actually the hook." Now, here is my point: Not all bails have hooks.
–
J.R.Mar 29 '13 at 18:02

@J.R., oh sorry for not being clear,and going to remove that comment, plus edit wherever was not clear enough, all i wanted was to give a quick idea but i also remember everywhere i used a reference from where i was mentioning[and in Matthew's answer the complete definition was from the source he mentioned]. Got your point though.
–
RaghavMar 29 '13 at 18:07